Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Oponente do San Francisco 49ers teve qual a semana mais baixa?
 ###Tabelas: CREATE TABLE engines_and_transmissions (engines_and_transmissions_id AUTO_INCREMENT PRIMARY KEY, Model/Engine VARCHAR, Capacity VARCHAR, Cylinders/Valves VARCHAR, Power/rpm VARCHAR, Torque (Nm)/rpm VARCHAR) CREATE TABLE schedule (schedule_id AUTO_INCREMENT PRIMARY KEY, Week INT, Date VARCHAR, Opponent VARCHAR, Result VARCHAR, Venue VARCHAR, Attendance INT) CREATE TABLE wins_by_club (wins_by_club_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Club VARCHAR, Wins INT, Last win INT, Runner-up INT, Last losing final VARCHAR) CREATE TABLE ships_of_the_class (ships_of_the_class_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Pennant number VARCHAR, Laid down VARCHAR, Launched VARCHAR, Date of commission VARCHAR, Homeport (as of July 2013) VARCHAR, Planned decommission (as announced in 2009) VARCHAR) CREATE TABLE day_2_evening_session (day_2_evening_session_id AUTO_INCREMENT PRIMARY KEY, Match no. INT, Match Type VARCHAR, Team Europe VARCHAR, Score VARCHAR, Team USA VARCHAR, Progressive Total VARCHAR)  
SELECT MIN Week FROM schedule WHERE Opponent = at san francisco 49ers